In resin-encapsulated integrated power devices, e.g., in so-called SIL (Single-In-Line) power devices, the semiconductor die is directly bonded onto the flat face of a heat sink metal baseplate, commonly a nickel or silver coated copper plate, which may or may not extend beyond the perimeter of the encapsulating resin body, which is molded on the face of the metal baseplate. Commonly, a projecting portion of the heat sink baseplate beyond the perimeter of the encapsulating resin body (or of an encapsulating metal enclosure) has the function of providing the means for mounting the device on an external heat sink or vice versa, with a good thermal coupling therebetween. In such a projecting portion of the baseplate one or more holes or slots are often formed for accommodating the stem of assembly screws or similar fastening means.
The metal pins for the electrical connection of the integrated circuit are derived from a die-stamped metal frame, commonly of copper, which may be coated with nickel, silver or gold. During the assembling stages of the device, the die-stamped metal frame is fastened to the heat sink metal baseplate by tab wedging or by laser welding, whereby at least one ground pin of the finished device is electrically in contact with the metallic heat sink baseplate, as is well known to the skilled technician. Therefore, the heat sink baseplate of the device is electrically connected through at least one of the pins of the device to a ground rail of the external printed card circuit. External heat sink plates mounted on the device are also customarily connected to a ground rail of the external printed card circuit.
The connection to ground of the metallic heat sink baseplate onto which the semiconductor die is directly bonded by means of a conductive adhesive, loaded with conductive metal powder (e.g., silver powder), or an eutectic lead and tin alloy, is commonly exploited for closing, through the heat sink baseplate itself, one or more electrical paths toward ground, by connecting with metal wires the respective metallicized pads for ground connection formed on the front of the die to the baseplate itself. When the die is relatively large, these ground connection wires tend to assume radiuses of curvature relatively small and because of the consequently increased mechanical stresses they often break near the welding point either during the resin encapsulation molding or during the normal operation of the device. Statistically their vulnerability is dramatically higher than that of the connection wires between the other pads of the device and the respective pins of the patterned metal frame.